The present invention relates to a digital transmission system, comprising a transmitter for transmitting to a transmission medium a digital signal representing a wideband digital signal having a specific sampling frequency F.sub.s and a bandwidth, and a receiver for receiving from the transmission medium a digital signal substantially corresponding to the digital signal representing the wide-band digital signal. The present invention also relates directly to the receiver.
Such a transmitter comprises (a) a first encoder unit for receiving the wide-band digital signal, the first encoder unit including (i) a sub-band coder unit for splitting up the bandwidth of the wide-band digital signal into M successive sub-bands which augment with frequency (each sub-band having a band number m, where m is an integer such that 1.ltoreq.m.ltoreq.M), and generating M sub-band signals having reduced sampling frequencies in response to the wide-band digital signal, each sub-band signal being made up of consecutive signal blocks which each contain q samples of that sub-band signal; (ii) a quantization unit for quantizing the samples in the signal blocks of the sub-band signals to produce quantized samples in the signal blocks; and (iii) a bit allocation unit for generating bit allocation information denoting how may bits the q samples in a signal block are quantized by; (b) a scale factor information generating unit for generating scale factor information relating to a scale factor for a signal block; (c) a combining unit for combining the quantized samples in the signal blocks, and the bit allocation information and the scale factor information relating thereto in successive frames of a second digital signal; (d) a second encoder unit for converting the second digital signal into a third digital signal which is error correction encoded; and (e) an application unit for applying the third digital signal to the transmission medium.
Such a receiver comprises (a) a receiving unit for receiving a replicated third digital signal from the transmission medium which substantially corresponds to the third digital signal applied thereto; (b) an error correction unit for correcting errors in and converting the replicated third digital signal into a replicated second digital signal which substantially corresponds to the second digital signal; (c) a control signal generating unit for generating a control signal if an error exists in the replicated third digital signal which cannot be corrected when the fourth digital signal is converted into the replicated second digital signal in the error correction unit; (d) an error masking unit for processing the replicated second digital signal in response to the control signal; (e) a derivation unit for deriving the quantized samples in the signal blocks of sub-band signals and the bit allocation information and the scale factor information relating thereto from frames of the replicated second digital signal to produce replicated samples in the signal blocks which substantially correspond to the original samples in the signal blocks of the sub-band signals; and (f) a synthesis filter unit for constructing a replica of the wide-band digital signal in response to the samples in the signal blocks.
A transmission systems of the type mentioned above is know from European Patent Application No. 402.973, which corresponds to U.S. Pat. No. 5,323,396. In such prior art receivers, if the received information contains one or more errors which cannot be corrected (i.e., one or more uncorrected errors), those errors are replaced by information obtained (i.e., error masking occurs) from interpolation of the received information. Separate interpolation circuits are necessary to enable application of such interpolation.